There are image forming apparatuses such as printers, facsimile machines, copying machines, plotters, and multifunction machines having function of these devices. Inkjet recording apparatuses are known as liquid ejection recording type image forming apparatuses that use a recording head for ejecting ink droplet. The liquid ejection recording type image forming apparatuses form an image on a sheet by ejecting ink droplets from a recording head onto the sheet being transported.
The image forming apparatuses of this type include serial type image forming apparatuses that form an image by ejecting liquid droplets from a recording head moving in a sub scanning direction and line type image forming apparatuses that form an image by ejecting liquid droplets from a stationary recording head.
The term “sheet” as used herein is not limited to paper but may be any substance, including OHP sheets, to which ink droplets or liquid can adhere. The “sheet” may also be referred to as a “to-be-recorded medium”, a “recording medium”, “recording paper”, and a “recording sheet”. The term “recording”, “printing”, and “imaging” may be used as synonyms for the term “image formation”.
The term “image forming apparatus” as used herein indicates a device that forms images by ejecting liquid onto media such as paper, strings, fibers, cloth, leather, metal, plastic, glass, wood, and ceramics. The term “image formation” as used herein indicates not only forming images that have meanings, such as characters and figures, on a medium, but also forming images that do not have meanings, such as patterns, on a medium (i.e., merely ejecting liquid droplets onto a medium). The “ink” is not limited to liquid that is commonly called ink but may be any material that turns into liquid when ejected. For example, ink may include DNA samples, resist, and patterning materials.
These liquid ejection type image forming apparatuses form an image by ejecting ink containing color materials in the form of liquid droplets. Therefore, problems such as feathering, which refers to dots of liquid droplets spreading to produce a feather-like edge, and color bleeding, which refers to a blurred border between colors due to adjacent different color ink droplets on a sheet being mixed, may occur. Moreover, it takes time for liquid droplets on a sheet to dry after printing.
Japanese Patent Laid-Open Publication No. 8-323977 (Patent Document 1) discloses a technique to prevent blurring using a heating device before or after printing and quickly dry ink after printing.
Japanese Patent Laid-Open Publication No. 2002-137378 discloses a technique to prevent blurring by applying a pretreatment liquid that reacts with ink using an application roller. Japanese Patent Laid-Open Publication No. 2005-138502 discloses a technique to apply a pretreatment liquid by ejecting the pretreatment liquid in the form of mist.
However, providing a heating device as in Patent Document 1 results in increased power consumption. On the other hand, using an application roller or a liquid ejection head as in Patent Documents 2 and 3 causes uneven application of a pretreatment liquid. Further, since the pretreatment liquid is in liquid form and therefore does not dry quickly after reaction with ink on a sheet, the sheet tends to be curled or warped, which often results in jamming.